Anybody who saw the Mavericks’ momentum-shifting, hope-inducing 103-99 win over Golden State on Wednesday no doubt recognized Shane Larkin’s speedball court-length drive in less than 3.9 seconds as a pivotal moment in the game.He would have had to slow down to be a blur.That play, more than any other, is why the Mavericks are growing quietly intrigued about the rookie guard’s future.Speed, as you may have noticed, has never been a strength of this franchise.In Larkin, they have a burner, basketball’s version of the deep threat. And the best news?“I honestly don’t feel like I’m back to my full quickness,” Larkin said. “I’ve got a ways to go to get back to where I was in college.”That’s a huge benefit of youth. When you are 21 years old, even surgery on your right ankle won’t slow you for long. And it’s reasonable to expect Larkin to be every bit as fast as he was before he broke a bone in that joint.His play at the end of the third quarter Wednesday was a much-needed moment for the Mavericks. And for Larkin, too. Coach Rick Carlisle has said the battle for backup minutes behind point guard Jose Calderon is robust between Larkin and fellow rookie Gal Mekel.Larkin has the built-in benefit that he also can put in a few minutes at shooting guard if need be. And, of course, he was the 18th overall pick in the draft. Mekel was an undrafted free agent. The Mavericks obviously have a bigger investment in Larkin.But Carlisle plays people on results, not reputations.That’s why he yanked Larkin after a cameo appearance Monday against Denver. He wasn’t seeing the aggressiveness that he needed to see.“Coach really sent me a message on Monday,” Larkin said. “I wasn’t being aggressive, didn’t play with a lot of energy. I was playing scared and nervous.”So Larkin changed things up and got rewarded with an extended run that led to seven points and six assists.